He made his debut for Tranmere at the age of 16. He progressed through the youth ranks at Tranmere and spent the last 18 months of his career at Prenton Park under the guidance of Brian Little. He featured as a substitute when they knocked out Merseyside rivals Everton in the 2000–01 FA Cup in a memorable 3–0 victory at Goodison Park.[2] Hume, who was linked with moves to Preston North End and Sheffield Wednesday prior to signing for Leicester, helped his previous club, Tranmere Rovers claim the scalp of Bolton Wanderers in an FA Cup campaign. He scored the winner in a replay at the Reebok Stadium as Tranmere went on to reach the quarter finals in 2004. His best season for Tranmere was during the 2004–05 campaign where he finished top scorer with 16 goals. Hume is a supporter of Liverpool and Hearts.[3]

Signed on transfer deadline day at the end of August 2005, Hume was Craig Levein's most expensive signing in his first year as manager. He was bought as a direct replacement for David Connolly who moved to Wigan the same day. Hume put pen-to-paper on a three-year deal after leaving Tranmere Rovers where he made 176 appearances, scoring 37 goals. The fee for Hume was an initial £500,000 that could rise to £750,000, while Tranmere were entitled to a 10% sell-on clause.[4]

Hume signed a new three-year deal on 5 June 2007 to stay at the club.[5] He scored his first goal of the 2007–08 season against Watford on 25 August,[6] and was named in the Championship Team of the Week two days later.[7] The goal was voted Goal of the Season on 28 April 2008.[8] Despite scoring a goal in his 100th match for Leicester on 11 December, his team still lost 3–1 to Ipswich.[9] Hume scored his 30th goal for Leicester on 16 February 2008, beating Norwich City 4–0.[10] Despite finishing as the club's top goalscorer with 11 league goals, Hume could not prevent Leicester from being relegated at the end of the season.

Despite announcing that he would stay at Leicester, on 25 June, Barnsley secured the signing of Hume for £1.2 million.[11] He signalled his intent to live up to the price tag he had been signed for. He was handed the new number 7 shirt, taking the number from Sam Togwell. On the opening day of the season, Hume scored just five minutes into his Barnsley debut away to Queens Park Rangers, however Barnsley lost the game 2–1. Hume was sent off on his home debut for Barnsley, a 2–1 defeat to Coventry City on 16 August 2008. He then scored his second goal for Barnsley in front of the Oakwell crowd with a stunning strike against Derby County. He then scored the 4th of Barnsley's 4–1 win over local rivals Doncaster Rovers, also at Oakwell, with a curling 30-yard strike past Neil Sullivan. He scored his fourth Reds goal in the home game with rivals Sheffield Wednesday. Barnsley ended up winning 2–1.

On 8 November 2008, he sustained a fractured skull and internal bleeding following an elbow to the head, prior to challenging for the ball, from Chris Morgan against Sheffield United. He was taken to hospital with life-threatening injuries. He underwent surgery after the incident.[12]

"Sheffield United are saddened and concerned to hear that Barnsley striker Iain Hume is being monitored in a high dependency unit following last Saturday's fixture, and we wish him a speedy and full recovery."[13]

On 11 November Hume was moved out of the high dependency unit at Manchester Hospital and into a normal ward. Reds manager Simon Davey visited Hume and said he was "in a bad way, very groggy, but talking". He was released from hospital on 17 November to continue his convalescence at home but subsequently re-admitted after feeling unwell. According to Sky Sports News this was due to an infection which was treated with antibiotics. Following due observation he was discharged once again. Hume subsequently returned to light training with the Barnsley squad participating in running and finishing activities.

Hume joined Preston on 14 September 2010, taking the number 16 shirt. He made his debut against Norwich and scored his first goal for the Lilywhites the following Saturday at Coventry, a right footed shot from 20 yards. He scored his second in as many games in the 6–4 win over Leeds United This pleased the fans a lot as it was the 10th goal of the match at Elland Road, securing the 3 points for Preston. On 23 October it was announced that Hume would return to Barnsley following a poor run of results for his parent club. However, on the 28th, Hume's loan was extended, with Paul Hayes going the other way to Barnsley with view to a permanent deal for Hume in January. Hume scored the winning goal for Preston on 11 December versus Ipswich Town and fellow international Jaime Peters, the game ended 1–0 with Hume scoring in the 50th. Hume scored against his old club, Leicester City with a half volley in the 90th minute of the game.

The Ipswich win was followed by a 14-game winless streak, which was broken by three consecutive wins over Scunthorpe, Coventry, and promotion hopefuls Swansea. Hume contributed a goal and an assist in the first two games, while scoring both against Swansea as Preston to a 2–1 win, the second goal coming after a mazy run past three defenders. After a loss to Reading, Hume was again on the scoresheet in the following game against Portsmouth that ended in an eventual 1–1 draw. At the end of the season, Preston were relegated to League One, following a dismal season with only 42 points.[15] Hume led the team with 12 goals in the Championship and became the first player from Preston following relegation to come out publicly committing himself to the team for the following season.[16]

Ahead of the 2011–12 season, he was awarded the vice-captaincy for his sheer effort and commitment to the club, although he shared that role with Graham Alexander until he was given the role of Joint Assistant Caretaker Manager, and he led the team out on their opening day defeat to Colchester United, which finished 4–2. After this, he scored goals against Crewe Alexandra, Scunthorpe United and Brentford.

In a match against Huddersfield Town, when he was not totally fit to play, he sustained an injury, which ended up keeping him out until December. He returned in a 0–0 draw with Stevenage, coming on at half time for an injured Paul Parry. His return was greeted warmly by the Preston fans. He scored his first goal since returning against Carlisle United, in a 3–3 draw on Boxing Day. Then after spending seven more weeks on the sidelines he scored two goals in the 2–1 win over Exeter.

On 31 August 2012, Hume signed for Doncaster Rovers on loan from Preston North End) until January 2013,[17] a deal that was extended till the end of the season. Hume made his debut for the club the following day as a second half sub for Kyle Bennett against Yeovil Town, the game ended in a 2–1 defeat.[18] Hume then went on to score in a 2–0 victory over Leyton Orient and also a crucial injury time winner against table toppers Tranmere Rovers. Hume's work ethic and skill soon made him become a fan favourite at the Keepmoat. He then later went to score in a 3–0 win over Hartlepool and then a crucial goal in the 3–2 win against Doncaster's local rivals; Scunthorpe United. Hume helped guide Doncaster Rovers to the league one title earning his first medal of his career and finished the 2012–2013 season with 7 goals.

On 21 August 2014, Hume was drafted by the Kerala Blasters, joining Player-Manager David James and Michael Chopra at the club.[20] Hume was the first player to score a goal for Kerala Blasters, which was against Chennaiyin FC, but they lost the match at last. His 2nd and 3rd goal of the season was against Atlético de Kolkata (in two different matches), where he was Hero of the Match in the first one. His fourth goal was against FC Pune City in the last group match of Kerala Blasters in the 2014 season, which was a winning goal and made Kerala qualify to the Semi-Finals. The First leg match against Chennaiyin FC, where Kerala saw their greatest victory so far (3-0). He was one of the three goalscorers of that match. In the same match, he assisted a stunning goal by Sushanth Mathew which was considered as the best goal by Kerala Blasters in that season so far.

Hume played at the 2001 FIFA World Youth Championship in Argentina, alongside Atiba Hutchinson and Mike Klukowski among others. He starred for Canada at the 2003 FIFA World Youth Championship. He scored three goals, including the game winner versus Czech Republic. The win over the Czech's qualified Canada for the round of 16, where they eliminated Burkina Faso on a goal by Josh Simpson. In the quarter finals, Hume scored the equalizer in the 53rd minute to send their game against Spain to extra time. Canada eventually bowed out to the Spanish by a 2–1 scoreline. It is Canada's best showing at a FIFA male event.

He made his senior debut for Canada in a February 2003 friendly match against Libya.

Coming on as a substitute in the 2007 CONCACAF Gold Cup semi-final versus the United States, he made an immediate impact, making his presence known through a few tough tackles and a remarkable goal, snapping Canada's 705-minute scoring drought in matches versus the United States. Minutes later he kept Canada within a goal's reach courtesy of a goal-line clearance with his heel, to deny Clint Dempsey a goal.